Foliage-sensitive bomb fuze



3,282,211 FGLIAGE-SENSHTHVE BOMB FUZE Edward T. Winston, Falls Church, Va., assignor to the United States of America as represented by the Secretary of the Army Filed Get. 7, 1963, Ser. No. 314,568 3 Claims. (Cl. 1027.4)

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to me of any royalty thereon.

This invention relates to projectile fuzes, and more particularly to a super sensitive impact fuze.

In many military tactical situations it is desirable to have a bomb fuze which will function just below the upper tree cover in order to maximize the destructive effect in wooded or jungle areas. Prior art impact fuzes are insensitive to contact with leaves, twigs, and other foliage, because the projectiles which house these fuzes are so heavy, relative to the leaves, twigs, etc., that the foliage fails to exert a suflicient retarding force to cause a function of the fuze.

Radio proximity fuzes, in some cases, are not suitable for jungle and forest use, both because of their high cost, and also because the foliage density varies greatly, precluding a reliable and uniform target signal.

It is, therefore, an object of this invention to provide a projectile fuze which can function on contact with light foliage such as leaves and twigs.

Another object of this invention is to provide an electromechanical fuze sensitive enough to be detonated by tree foliage, and yet is simple, reliable, and inexpensive.

A further object of this invention is to provide an impact fuze system which will produce air bursts just under a tree canopy when released on jungle or wooded targets, and which will produce a burst at ground level when released over open target areas, without requiring that the fuze be specially set for the type of terrain bombed.

These and other objects of this invention are achieved by mounting an impact-sensitive member on a flexible wand extending out from the projectile. In a specific embodiment, a plurality of inertia switches are mounted at the end of a plurality of flexible wands which extend radially from the bomb. The force exerted when the wand strikes a leaf, or other light foliage, is adequate to cause suflicient deceleration of the wand-mounted inertia switches, although this impact is not sufficient to cause an appreciable deceleration of the bomb itself.

The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

FIG. 1 is a pictorial view of a bomb with wand-mounted fuze switches in place.

FIG. 2 is a partial sectional view showing a wandmounted fuze switch in place.

FIG. 3 is a schematic diagram of one specific embodiment of this invention.

Referring now to FIG. 1, there is shown a bomb It with three foliage-sensing wands 11a, 11b, and 110, mounted thereon. The exact number of wands is, of course, a matter of choice. One is sufficient. However, three or more wands are usually desirable to give greater reach, and insure that the bomb does not pass through an opening in the tree cover. The bomb shown in FIG. 1 has stabilizing fins 12, as is common in the art.

In storage and transportation the foliage-sensing wands 11 may remain extended as shown in FIG. 1, since the projectile will be provided with a standard safety-andarming mechanism, as is conventional in the art. How ever, in many applications it will be more convenient to bend the wands 11 back, parallel to the body of the bomb, hold them in place with a strap, and release them when the bomb is dropped or fired.

As shown more clearly in FIG. 2, the foliage-sensing wands 11 consist of a flexible rod 13, with a trembler switch 14 mounted thereon. The rod may be made from any suitable material, although spring steel is highly satisfactory. The trembler switch 14 is a commercially available, inertially operated switch, consisting essentially of a conducting case 15 with an inertial mass 16 mounted on a flexible cantilever beam 17. The mass 16 is insulated from the can 15 in the rest position, and the switch is closed when the inertial mass 16 bends over and contacts the can 15. The trembler switch leads are indicated at 18.

The accelerating force needed to close the trembler 14 may be varied, but common practice dictates the use of a switch in the neighborhood of 30 times the force of gravity (30 g) in order that the switch will not be too sensitive to vibrations encountered in transportation and flight. That is, the trembler switch 14 must be accelerated at a rate 30 times greater than the acceleration produced by the force of gravity to cause it to close. The force required to produce the required acceleration of a 30 g trembler switch, when the switch is rigidly mounted with the body of the bomb 10, is:

f=ma

1 where,

For a ZO-pound bomb, with a 30 g trembler switch, the force needed is approximately 600 pounds. Of course, a leaf or twig cannot ordinarily develop the 600-pound reaction force which is necessary to close the switch and detonate the bomb when the inertia switch is carried in the bomb.

By moving the mass of the inertia switch 14 away from the mass of the bomb 10, and providing a flexible mount for the switch 14, applicant has provided a fuze which will detonate upon impact with foliage. With the 30 g trembler switches mounted on spring Wheel beams 13, the force (f necessary to close the wand-mounted trembler switch is:

f1= 1 +y where,

m =the mass of the trembler switch 14+ /3 of the mass of the beam 13, i

a the acceleration needed to close the switch (30 g),

k=the spring constant of the wand,

y=the deflection of the wand at impact.

A typical value of spring constant for a three-inch wand is 0.8333 pound per inch, a typical value for m would be 0.0026 pound, and a typical beam deflection would be 1.0 inch. With these values Equation 2 shows that a force of 0.91 pound is required to operate the 30 g trembler switch. Such a force is easily attainable from impact between foliage and a 20-pound bomb having a velocity of 400 to 600 feet per second.

FIG. 3 is a specific embodiment of a bomb using the teachings of this invention, which will detonate below the foliage canopy in a jungle or wooded area, and will detonate immediately upon impact with the ground in open areas without separate settings for the two conditions. The embodiment of FIG. 3 employs three wandmounted foliage-sensitive switches 11a, 11b, and mounted substantially in the configuration shown in FIG. 1. These switches 11 are connected in parallel to a delay detonator 21. The delay detonator 21 provides a sufficient delay to cause the bomb to detonate just below i i arming mechanism.

thefoliage cover after being triggerediby a, leafor twig.

high inthe cover.

In the embodiment of FIG. 3 an additional impact =sWitch 22 is provided'withinthe bomb 10, This switch 22 may also be a trembler switch, 'and'ismounted inside.

' the bomb 1t connected to an instantaneous detonator 23. The switch 22 will be insensitive to impact between the bomb and foliage or twigs since, for a 3-0 g switch, a forceof 600 pounds is required; as outlined above. The purpose of 'switch'22 and the instantaneous detonator 23 is to provide a-burst at ground level in the event the bomb is dropped in an open area.

- Any of a number of conventional systems are suitable for use with this invention. The embodiment of FIG. 3 shows a vane-operated safety-and- In flight, rotation of the vane 24 closes theair arming switch 25 connecting-the trembler switches 11 and 22 to apower supply 26. Additionally,

a conventional 'out-of-line safety-and-arming system may i be provided between the detonators 21: and 23 and the high explosive in the bomb.-

It Will be apparent that the embodiments shown are exemplary and that various 'modificationscan. bemade in construction and arrangement within the scope of the invention as defined in the appended claims i I claim as my invention: 1. A high-explosive projectile comprising: (a) a body havingan explosive charge therein,

(b) an electrically-operable exploding means for said charge, (c) a source of electrical power,

safety-and-arming i- -(d) a plurality: of flexible wands extending radially from said body,

(e) an inertial switch mounted at the extremity of I i each ofsaid Wands away from said body, said inertial switch including an inertial member movable reiaresponse to relative: motion of said members, :and

(i) an electrical circuit connecting said source to said exploding means through said switch; i 0 (g) whereby electricalcurrent isvapplied to said exploding means in response to closing of said'switch.

- 2.: A projectile according to claim 1, wherein said detonator.

lnstantaneous electrical detonator rigidly attachedito said body.

, j keterencesfited by the Examiner. i

SAMUEL FEINBERG, Primary Examiner.

BENJAMIN A. BORCHELT, Examiner.

' W.-C. ROCH, Assistant Examiner.

- tive to another member toclose an electric circuit in s electrically/operable exploding means includes a delay- 3. A projectile according to claim 2 having a second UNITED STATES PATENTS 3 

1. A HIGH-EXPLOSIVE PROJECTILE COMPRISING: (A) A BODY HAVING AN EXPLOSIVE CHARGE THEREIN, (B) AN ELECTRICALLY-OPERABLE EXPLODING MEANS FOR SAID CHARGE, (C) A SOURCE OF ELECTRICAL POWER, (D) A PLURALITY OF FLEXIBLE WANDS EXTENDING RADIALLY FROM SAID BODY, (E) AN INERTIAL SWITCH MOUNTED AT THE EXTREMITY OF EACH OF SAID WANDS AWAY FROM SAID BODY, SAID INERTIAL SWITCH INCLUDING AN INERTIAL MEMBER MOVABLE RELATIVE TO ANOTHER MEMBER TO CLOSE AN ELECTRIC CIRCUIT IN RESPONSE TO RELATIVE MOTION OF SAID MEMBERS, AND (F) AN ELECTRICAL CIRCUIT CONNECTING SAID SOURCE TO SAID EXPLODING MEANS THROUGH SAID SWITCH, (G) WHEREBY ELECTRICAL CURRENT IS APPLIED TO SAID EXPLODING MEANS IN RESPONSE TO CLOSING OF SAID SWITCH. 